DK-B-109 591 discloses a bag of the type stated in the introduction formed as a tobacco pouch having a pouch portion formed by folding a flexible packing material onto itself, and a flap folded down over the pouch portion. The inner face of the flap is welded or adhered peelably to the outer face of the pouch portion by means of a longitudinal weld, while the inner faces of the opposite walls of pouch portion and the flap are welded together in a non-peelable manner. This is obtained by using a packing material having a heat sealable first surface providing a fusion seal, when sealed onto itself, and a second surface providing a peel seal, when sealed onto the heat sealable surface of the packing material.
As examples of possible combinations of the two surfaces of the packing material polyethylene and vellum paper as well as polyethylene and aluminium foil are mentioned. When sealing polyethylene to vellum paper, a gas-proof packing cannot be obtained due to the structure and surface of the latter material. When sealing polyethylene to aluminium foil, an adhesion is obtained, whose strength is very difficult to control. In said publication it is therefore suggested to use an adhesion seal between the two materials of the mentioned combination of material.
The bags are made as single-bags, which are open at one side edge, i.e. only the longitudinal peel seal and one of the non-peelable seals are made, whereafter the prefabricated bags are filled with the desired product and the second strong side seal is provided. This method does not meet the requirements of today for a rational packing of products.
Peelable bags made on automatic form and fill machines are known. However, in these known bags the peelable seal is a side edge weld, i.e. the weld on which the product falls, when it is filled into the partly finished packing. This causes major problems, as the weld has to have such a strength when hot (hot tack strength) that it does not break, when the product falls thereon, but at same time it should be peelable when cold.
Finally, it should be mentioned that packing materials are known having a first outer layer of a copolymer of a polyethylene and polypropylene and a second outer layer of a polyethylene-containing polymer.